Multiple Forms of Leucyl sRNA Synthetase of E. coli

Multiple species of sRNA for a single amino acid have been demonstrated by a number of investigators. In the case of leucine-specific sRNA of E. coli, four or five fractions were obtained by counter-current distribution (Goldstein et al. 1964; Apgar and Holley, 1964). These leucine sRNAs can be distinguished from each other by their capacity to accept leucine from a homologous enzyme only, or from homologous as well as heterologous enzymes; or by their preferential response to a specific messenger RNA containing either U, or UG, or UC monomers (Bennett et al., 1963, 1965; Weisblum et al., 1962, 1965). These observations immediately raised the question whether there are multiple species of the corresponding enzyme, the aminoacyl sRNA synthetase.